A magnetic resonance imaging (MRI) system includes various coils such as, for example, body coils covering the whole body, local coils covering only a certain part of the body, and so on. A body coil is a self-transmitting and self-receiving coil. Since the coverage of a body coil is relatively large, a higher transmit power is to be provided, and the signal to noise ratio of the resulting image is lower. The signal to noise ratio is not uniform throughout the image. Since the coverage of a local coil is relatively small (e.g., the knee covered by a knee coil, the head covered by a head coil, and the wrist covered by a wrist coil are all relatively small ranges), the local coil only receives radio frequency signals within a limited range of radio frequency excitation (e.g., in order to distinguish from radio frequency signals in the transmission stage, the radio frequency signals received by the coil are hereinafter referred to as magnetic resonance signals). Therefore, the signal to noise ratio of the resulting image is relatively high, and the signal to noise ratio is relatively uniform throughout the image.
Orthopedic imaging is an important direction of magnetic resonance application. In an orthopedic imaging clinical application of the magnetic resonance system, shoulder joint inspections use high quality images. Because of the complex structure of the shoulder joint, in order to obtain high quality shoulder joint images, specifically designed coils may be used. In order to make a patient feel comfortable and take the particularity of the position of the shoulder into consideration, the shoulder coil may be placed at the edge of a sickbed. The edge of the sickbed may be the edge that is close to a uniform magnetic field area, and the uniformity of the static magnetic field and the radio-frequency magnetic field of the edge area will be both reduced. This will cause image shape distortion or image quality degradation.
Coils currently used in magnetic resonance systems for accepting shoulder joint imaging may be phased array coils used as receiving coils. On the market, there are many special receiving phased array receiving coils for shoulder joint imaging. Receiving phased array coils are a collection of several closed receiving elements. Each coil unit receives signals via a low-noise preamplifier and an independent receiving channel and performs post-processing on the signals. In this way, images of a high signal to noise ratio, a small coil unit and a relatively large imaging area (FOV) may be obtained.
Transmitting/receiving coils combined by transmitting coils and receiving coils have been widely used in the magnetic resonance system. In the condition of using the same transmit power, compared with receiving phased array coils, transmitting/receiving coils may generate a radio-frequency magnetic field of a high intensity and high uniformity in the focusing area. This is because the transmitting/receiving coils have a special transmitting part that improves the transmission efficiency, which brings many beneficial effects to the application of the magnetic resonance system.
Transmitting/receiving coils that have a dedicated transmission cable for connecting to the magnetic resonance system use a high-power capacity switch circuit and a power distribution circuit. Although the design difficulty decreases, the costs of the coils and the system are greatly increased.